Business, science and entertainment applications depend upon computing systems to process and record data, often with large volumes of the data being stored or transferred to nonvolatile storage media, such as magnetic discs, magnetic tape cartridges, optical disk cartridges, floppy diskettes, or floptical diskettes. Typically, magnetic tape is the most economical and convenient means of storing or archiving the data. Storage technology is continually pushed to increase storage capacity and storage reliability. Improvement in data storage densities in magnetic storage media, for example, has resulted from improved medium materials, improved error correction techniques and decreased areal bit sizes. The data capacity of half-inch magnetic tape, for example, is now measured in hundreds of gigabytes on 896 or more data tracks.
FIG. 1 illustrates a traditional flat-lapped bi-directional, two-module magnetic tape head 100, in accordance with the prior art. As shown, the head includes a pair of bases 102, each equipped with a module 104. The bases are typically “U-beams” that are adhesively coupled together. Each module 104 includes a substrate 104A and a closure 104B with readers and writers 106 situated therebetween. In use, a tape 108 is moved over the modules 104 along a tape bearing surface 109 in the manner shown for reading and writing data on the tape 108 using the readers and writers 106. Conventionally, a partial vacuum is formed between the tape 108 and the tape bearing surface 109 for maintaining the tape 108 in close proximity with the readers and writers 106.
FIG. 2A illustrates the tape bearing surface 109 of one of the modules 104. The tape 108 is shown in dashed lines. The module is long enough to be able to support the tape as the head steps between data tracks.
As shown, the tape 108 includes four data bands (Band 0-3) that are defined between servo tracks 202. Each data band may include a number of data tracks, for example 224 data tracks (not shown). During read/write operations, the elements 106 are positioned within one of the data bands. Outer readers, sometimes called servo readers, read the servo tracks 202. The servo signals are in turn used to keep the elements 106 aligned with a particular track during the read/write operations. Typically, a coarse positioner (worm gear, etc.) places the head generally adjacent a given data track, then a fine positioner (voice coil, etc.) keeps the heads aligned using the servo tracks.
FIG. 2B depicts a plurality of read/write elements 106 formed in a gap 208 on the module 104 of FIG. 2A. As shown, the array of elements 106 includes, for example, sixteen writers 209, sixteen readers 210 and two servo readers 212. As noted by considering FIGS. 1 and 2A-B together, each module 104 will include a complementary set of elements 106.
One designing magnetic storage systems, such as tape storage systems, strives to increase the data density of the medium. As a means for adding more data to a given area of a magnetic medium, succeeding generations of tape formats are born. Typically, newer formats may include more data bands as well as more data tracks per data band and/or width of the tape, and also improvements in data linear density.
On any head, both the spacing between the elements and the element dimensions conform to a particular tape format. Usually, a head designed for one format will not work with a tape written in another format, as the servo readers usually will not align with the servo tracks. In addition the data elements may not align with the written tracks. Accordingly, one wishing to keep data stored on a magnetic medium in one format but wishing to move to equipment in a new format must either keep an operational drive designed for the earlier format, or transfer the data to a medium in the new format.
One known attempt to provide a multi-format head 300 is shown in FIG. 3. As shown, the head 300 includes four modules 302A, 302B, 303A, 303B aligned parallel to the direction of tape travel. The outer pair of modules 302A, 302B each have an array of elements 304A, 304B arranged according to a first tape format, while the inner pair of modules 303A, 303B each have an array of elements 306A, 306B for a second tape format, the second tape format different than the first tape format. In both pairs, the complementary elements (304A with 304B, 306A with 306B) are displaced from each other in the direction of tape travel. However, these types of heads are very expensive to manufacture, as several independent modules 302A, 302B, 303A, 303B must first be fabricated. Also, once manufactured, the modules 302A, 302B, 303A, 303B must be precisely aligned, considering the critical wrap angles between the modules as well as the outer wrap angles. In addition, because of the larger spacing between the outer modules 302A, 302B, the head will be more susceptible to errors due to tape wobble. For example, in read-while-write operation, the readers on the trailing module 302B read the data that was just written by the leading module 302A so that the system can verify that the data was written correctly. If the data is not written correctly, the system recognizes the error and rewrites the data. However, the tape does not move across the head perfectly linearly. Rather, the tape may shift back and forth, or “wobble,” as it crosses the tape bearing surfaces, resulting in dynamic skew, or misalignment of the trailing readers with the leading writers. The farther the readers are behind the writers, the more chance that track misregistration will occur. If it does occur, the system may incorrectly believe that a write error has occurred.
Another known attempt to provide a multi-format head 400 is shown in FIG. 4. This tape head 400 is configured as a Read-Read-Write (R-R-W) head. Tape head 400 includes merged primary tape format read/write elements 404A, 404B and secondary tape format read elements 406A, 406B on each module 402A, 402B. In this instance, head 400 is capable of reading a secondary format corresponding to secondary format read elements 406A, 406B. Head 400 is further capable of both reading and writing with the primary format corresponding to primary read/write elements 404A, 404B.
With continued reference to FIG. 4, the primary and secondary elements 404A, 404B, 406A, 406B are aligned parallel to the direction of tape travel. Typically, each row of elements is fabricated in sequential fabrication sequences. For example, elements 404A, 404B may be formed first. Then the secondary elements 406A, 406B are fabricated above the primary elements 404A, 404B. However, this type of “stacked” head is complex and expensive to fabricate, as each row of elements 404A, 404B, 406A, 406B must be fabricated independently. Further, an error in processing late in the fabrication process can result in an expensive loss. Additionally, the electrical connections that would be necessary to traverse the multiple layers for so many devices would be very complex.
In addition to fabrication issues, modules implementing stacked rows of element also suffer from reliability issues. For instance, the head will run hotter, as the heat sinking effect of the substrate will be reduced. Particularly, if the upper array is being used, heat will have to travel through several layers of devices do reach the substrate. A further issue is the thick gap that would be required in order to accommodate stacked arrays. Tape irregularities tend to droop slightly into this gap and erode the elements. This produces head-tape spacing problems, such as declining signal resolution. Gap wear can also lead to debris deposition issues such as shorting.
There is accordingly a clearly-felt need in the art for a magnetic head assembly capable of reading and/or writing in multiple formats, yet that is simple and less expensive to manufacture. It would be desirable to be able to read and write multiple formats for such things as backward compatibility, as well as compatibility across competing formats.